The invention relates to a method for controlling and/or regulating the drag torque in a drive train. More specifically, the invention relates to a control and/or regulating system that is assigned to a drive train for controlling and/or regulating the drag torque.
Methods for regulating the drag moment in drive trains of various designs are well known, and these especially include diesel-electric drive trains, but also conventional mechanical drive trains in various forms. In a conventional drive train with an internal-combustion engine and a mechanical drive train that comprises a gearbox unit connected to the engine, during the drag operation mode phase, a reversal of the energy flow occurs, i.e., power from the wheels is introduced into the vehicle, and serves the purpose of driving the drive train from the wheels to the internal-combustion engine. The document DE 43 34 210 A1 discloses a control system that can be used to operate an assembly for a vehicle, preferably a motor vehicle, in which at least a clutch is provided between an internal-combustion engine and a gearbox unit. In order to save fuel, by using a drive assembly of this kind in tandem with a control computer, during the drag operation mode phase, the drive engine is uncoupled from the gearbox unit and shut down. In order to end the drag operation mode phase, it is sufficient to actuate the foot throttle with a certain deflection angle and/or a certain speed of change in the deflection angle. In order to prevent a knowledgeable driver from knowingly interrupting the drag operation mode phase (and thus increasing the fuel consumption) by prematurely actuating the foot throttle, which would create an engine-braking effect for a short period, DE 43 34 210 A1 proposes to continuously measure the rotational speed of the gearbox's outgoing shaft and the position of the control lever during the drag operation mode phase and to assign the results to a reference value stored in computer memory. A subsequent comparison of this value, which characterizes the position of the foot throttle, makes it possible to re-engage the above-mentioned clutch during the drag operation mode phase only when the determined position of the foot throttle matches the actual position of the foot throttle. Thus, the fuel-saving effect is achieved by uncoupling the drive engine. However, it requires the actuation of at least one control element, and the drag operation mode itself cannot be influenced, especially in regards to the speed of the vehicle. When travelling downhill, this solution is especially disadvantageous, because it does not allow one to utilize the braking moment of the inertia of the internal-combustion engine. Therefore, this solution requires actuating additional braking equipment to avoid undesired acceleration. Furthermore, in this design, the internal-combustion engine is always uncoupled, irrespective of whether the engine braking moment can be utilized positively or negatively.